The function is .

From the graph,  is increasing over .

From the graph,  is decreasing over .

Now find open interval analytically.

Apply derivative to find the critical numbers.

Equate it to zero.

Therefore the critical number is .

Consider the test intervals to find the intervals of increasing and decreasing.

Consider a number in the interval .

Let .

Sign of  is negative, hence  is decreasing over .

Consider a number in the interval .

Let .

Sign of  is positive , hence  is increasing over .

 is increasing over .

 is decreasing over .